The whole first DP series (DP1/DP1s/DP1x/DP2/DP2x) was
plagued by an incorrect implementation of bracketing for
long time exposures: only the correctly exposed image was
corrected with dark frame subtraction:

I have now tested bracketing with the DP2M, and I am happy
to report, that this problem has been
fixed
! Of course
bracketed long time shots now take longer, since the dark
frames for all 3 exposures need to be captured as well.